The invention relates to a hydraulic system for a vehicle, such as an agricultural tractor.
Current production agricultural tractors have hydraulic systems which typically have an engine driven pump near the engine at the front of the tractor, a hydraulic oil cooler at the front of the tractor, hydraulic components, such as steering and brake system components at the middle and rear of the tractor, hydraulic components, such as hitch system components and selective control valves at the rear of the tractor, and a filter in the pump inlet line. Typically, the steering system hydraulic components are connected in series between the pump and the oil cooler. Such a system requires multiple hydraulic lines to connect the hydraulic oil cooler at the front of the tractor to the components at the middle and rear of the tractor. These lines take up space in the operators compartment and in other parts of the tractor. Also, when starting the tractor in cold weather, with the filter in the pump inlet line, the hydraulic pump can cavitate, and this can cause noise, temporary loss of performance and can damage the pump.
Accordingly, an object of this invention is to provide a tractor hydraulic system with fewer hydraulic lines between the hydraulic oil cooler at the front of the tractor and the components at the middle and rear of the tractor.
A further object of the invention is to provide such a tractor hydraulic system which substantially or greatly reduces the tendency of the system to cavitate.
These and other objects are achieved by the present invention, wherein a hydraulic system is provided for a vehicle having front, middle and rear portions. The hydraulic system includes a main pump located in the front portion, and a secondary pump located in the front portion which supplys fluid to an inlet of the main pump and to lube circuits. High pressure hydraulic functions are located in the middle and rear portions and receive high pressure fluid from the main pump. A hydraulic filter is located in the front portion and is connected to an outlet of the secondary pump for filtering fluid communicated to the inlet of the main pump. A relief valve is located in the front vehicle portion and is connected between the outlet of the secondary pump and the hydraulic filter. An inlet suction screen is located in the rear portion and is connected between a sump and the inlet of the main pump. An oil cooler is located in the front vehicle portion and is connected between the hydraulic filter and an inlet of the main pump.